This invention relates in general to electrography and, more specifically, to a flexible, curl resistant electrographic imaging member.
In the art of electrography, an electrostatic latent image is formed on a dielectric imaging layer (electroreceptor) by various techniques such as by an ion stream (ionography), stylus, shaped electrode, and the like. Development of the electrostatic latent image may be effected by the application of electrostatically charged marking particles.
Ion stream electrographic imaging may be accomplished with the aid of ion projection heads. Movement of the ion stream may be assisted by means of a fluid jet introduced into an ion projection head. For example, fluid jet assisted ion projection heads in electrographic marking apparatus for ion projection printing may utilize ions generated in a chamber, entrained in a rapidly moving fluid stream passing into, through and out of the chamber, modulated in an electroded exit zone by being selectively emitted or inhibited therein, and finally deposited in an imagewise pattern on a relatively movable charge receptor (electroceptor). More specifically, the ion projection head may comprise a source of ionizable, pressurized transport fluid, such as air, and an ion generation housing, having a highly efficient entrainment structure and a modulation structure. Within the ion generation housing there is a corona generator comprising a conductive chamber surrounding a wire, and an entrainment structure which comprises an inlet opening for connecting the source of ionizable fluid into the chamber and for directing the fluid through the corona generator, and an outlet opening for removing ion entraining transport fluid from the chamber. The exiting ion laden transport fluid is directed adjacent to the modulation structure for turning "on" and "off" the ion flow to the charge receptor surface. The chamber, the corona generating source, the inlet opening, the outlet opening and the modulation structure each extends in a direction transverse to the direction of relative movement of the electroceptor. The electroceptor may be uniformly charged by suitable means such as a corona charging device, brush charging, induction charging devices and the like, prior to imagewise discharge of the uniformly charged electroceptor by means of a fluid jet assisted ion projection head. In conventional xerography, corona charging is carried out with a device having a high charge output and a large opening such as a corotron so that a high voltage may be deposited on thick photoconductive insulating layers. A thin electroceptor of less than one half mil having a dielectric constant of about 2 or 3 will not charge up to high electric potentials used in conventional zerography on thick photoconductive insulating layers. Thus, if such an electroceptor is employed in an ordinary ion projections electrographic printing system and is uniformly charged with a device having a high charge output and a large opening such as a corotron, it cannot be charged to high electric potentials. In ionographic systems utilizing fluid jet assisted ion projection heads, only a small amount of ions are emitted due to modulation requirements. Therefore, imagewise discharge of a uniformly charged electroceptor by means of a fluid jet assisted ion projection head results in only a slight change in potential and development density of the electrostatic latent image is poor due to low contrast potential. In U.S. Pat. No. 4,524,371 to N. Sheridon et al, issued June 18, 1985, a fluid jet assisted ion projection printing apparatus is described comprising a housing including ion generating and ion modulating regions. The fluid jet dislodges ions from an electrically biased wire and requires high flow rates to achieve higher deposited charge density. Fluid jet assisted ion projection printing systems are well known and described, for example, in U.S. Pat. No. 4,463,363, U.S. Pat No. 4,524,371 or U.S. Pat. No. 4,644,373. The entire disclosures of U.S. Pat. No. 4,463,363, U.S. Pat. No. 4,524,371 and U.S. Pat. No. 4,644,373 are incorporated herein by reference. If desired, other means such as a stylus, instead of fluid jet ion projection, may be used to charge an electroceptor.
Electrographic imaging members and electrographic methods of using the members are well known and disclosed, for example in the patent literature and also in copending U.S. patent application Ser. No. 07/459,401, filed on Dec. 29, 1989 in the name of J. Frank et al, the entire disclosure of this copending application being incorporated herein by reference.
Some prior art xerographic photoreceptors having a thickness of at least about 25 micrometers (1 mil) have been charged to relatively high voltages because of an unlimited power source such as a corotron which are not charge limited. Unfortunately, xerographic photoreceptors require expensive special shipping and storage treatment for protection from temperature extremes or fluctuations, exposure to sun light, contact with reactive fumes and the like. Moreover, special shutter systems, particularly automatic shutter systems, are required in xerographic machines to protect the photoreceptor when it is in use or when it is not in use. Further, photoreceptors are usually sensitive to heat and must be located a safe distance from fusers thereby limiting flexibility in machine architecture design. Also, photoreceptors are sensitive to toner filming, fatigue and surface cracking. In addition, the coefficient of friction, surface energy and the like of photoreceptors materials, particularly the surface, cannot be readily tailored to accommodate different machine components such as blade cleaning systems. Moreover, cycle up and cycle down problems are a common characteristic of photoreceptors.
A dielectric layer for use in electrography may be a homogeneous layer of a single material such as a film forming polymer or inorganic solid or it may be a composite layer containing a particulate dielectric material dispersed in a continuous dielectric matrix material. Generally, the dielectric layer is supported on a layer comprising an electrically conductive material. The electrically conductive material may, in turn, be supported on a supporting substrate or the electrically conductive material may itself form the supporting substrate. The supporting substrate may be rigid or flexible.
When flexible substrates for electrographic imaging belts for electrography are coated with a dielectric layer and the applied coating is dried at an elevated temperature, the edges of the resulting belt curl upwardly when the belt is cooled to ambient temperatures. Such curling is undesirable because the uneven surface of the imaging member interferes with optimum formation of electrostatic latent images, particularly when the images are formed by ionographic imaging techniques. Moreover, curled electrographic imaging surfaces adversely affect the quality of the toner images formed during development. Moreover, such uneven surface of the imaging member can cause incomplete or partial transfer of the toner image to receiving members. A curled flexible electrographic imaging member requires considerable tension to flatten the member against a supporting member before sufficient flatness can be achieved. This can result in the development of an excessive amount of creep and may even cause tearing.